Heretofore water-based inks used in various writing intruments such as founting pens, felt pens, or draftman's pens as well as those used in ink-jet plotter or printer machines for information recording purposes have the conventionally contained a water-soluble dye. Such water-based inks containing water-soluble dyes, however, have the defect that when writing or printing with such inks, letters or printed objects may often become blurred. Furthermore, they are not water-resistant and durable even after drying. Japanese Kokai (laid open) Patent Application No. 172076/87 discloses a water-based ink produced by adding an oil-soluble dye dissolved in an organic solvent to an aqueous suspension of a water-insoluble polymer, and allowing the oil-soluble dye to diffuse into the polymer particles. According to this technique, however, it is not possible for the polymer particles to carry an amount of dyes desirable for imparting the ink with optimal chromatic parameters. This is because the diffusion coefficient of particular dyes is the limiting factor. Japanese Kokai (laid open) Patent Application No. 273274/87 proposes a water-based ink employing pigments as a colorant. This ink comprises a polymer dispersion produced by emulsion polymerizing monomers in the presence of a protective colloid but the polymer particles themselves are discrete from the pigment particles. Thus, they are susceptible to phase separation upon storage.
A need exists for a water-based ink which eliminates or ameliorates various defects of the prior art water-based inks noted as above.